The present invention relates to a testing apparatus for the purpose of testing for defects in liquid crystal display substrates used in liquid crystal display panels and the like.
Active matrix liquid crystal displays have been used in the realization of liquid crystal display panels having a high number of pixels for use in liquid crystal displays, including televisions or the like. These have a construction which is provided with switching circuits which operate by using thin film transistors to drive the various pixels. The number of pixels generally reaches 250,000 to 500,000, and units with more than 1,000,000 have reached the marketplace.
Conventionally, in the manufacturing of liquid crystal display panels of this type of active matrix, a process has been used in which first pixel electrodes corresponding to each pixel are disposed in a matrix form on a substrate of glass or the like, and by means of the formation of gate lines and source lines which are connected to each of these pixel electrodes and thin film transistors corresponding to each of these pixel electrodes, an active matrix liquid crystal display substrate (hereinafter shortened to "liquid crystal substrate") is manufactured. Next a transparent substrate is disposed above this liquid crystal substrate and facing it through the medium of a space, and the gap formed between the liquid crystal substrate and the transparent substrate is filled with liquid crystal.
This type of liquid crystal substrate comprises a plurality of pixel electrodes and lines corresponding thereto, as well as thin film transistors, are all manufactured in clean rooms which are so controlled by means of various layer formation processes so as to contain an extremely small amount of dust. However, in liquid crystal substrates with a large number of pixels, the size of each pixel and the widths of the lines are extremely fine, so that the presence of a small amount of microdust included in the manufacturing atmosphere is directly connected to the quantity of open-circuit defects or short circuit defects of the gate lines or the source lines, or the like. In addition, a maximum defect level is permitted on each liquid crystal substrate. Liquid crystal substrates with extremely large numbers of pixels are manufactured with the current manufacturing technology, it is extremely difficult to keep the number of defects below the permitted limit, and the rate of unacceptable units is remarkably high.
Moreover, in the case of the manufacture of liquid crystal substrates of the above type, it is necessary to test for defects in the manufactured liquid crystal substrates, however, conventionally, in the manufacturing process of the liquid crystal substrates, there was no effective technique for the testing of defects in the liquid crystal substrates themselves, and as a result, only after the completion of the liquid crystal display panel was a test conducted by supplying an electric current through the liquid crystal display panel and observing whether each pixel actually functioned or not. At this point, even if defects were detected by the testing, it was difficult to conduct repair or the like on the liquid crystal substrates and thus the products had to be rejected and disposed of, and this was a factor which prevented an improvement in the rate of acceptable products among active matrix liquid crystal display panels, and a lowering of the manufacturing costs thereof.